Automated media libraries typically use one or more movers, e.g., robots, to access media devices, e.g., tape cartridges, that are stored within the automated media library. For example, a single mover, robot or media changer device can be utilized to access media devices that are stored within the automated media library. Alternatively, multiple or redundant movers, robots or media changer devices can be utilized in an automated media library, which operate in either an active/passive mode or an active/active mode.
During operation of the automated media library, e.g., an automated tape library, one or more of the movers can move between a status of being available and a status of being unavailable, such as due to failure, scheduled maintenance, etc. As utilized herein, the term “available” with regard to the movers signifies that the movers are ready and able to be used at that time to perform operations and/or command requests, e.g., motion requests for accessing certain specific storage media within the automated media library, from host applications, users, etc. Conversely, as utilized herein, the term “unavailable” with regard to the movers signifies that the movers cannot be used at that time to perform operations and/or command requests from host applications, users, etc. due to mover transition. Moreover, as utilized herein, the term “mover transition” signifies the period of time when one or more movers or robots are temporarily unavailable for use due to failure (in a multiple mover system), scheduled service, repair or maintenance, or other applicable reasons that are generally known in the industry.
In a single mover system, the mover or robot may periodically require service, repair or replacement, i.e. the mover or robot may periodically move to a status of unavailable. Traditionally, automated media libraries use two main approaches to service, repair or replace a failed mover system in an automated media library. The first approach requires the customer to plan for downtime or an outage and the system would usually be taken out of service for a period of time to allow for the repair action. Such an approach requires a “service window” or “outage” where the host application will need to take the library offline and not schedule any operations, as any such operations would fail during the service window. The second approach requires the failed mover to be moved into a separate service area where it will be secured and shielded from other robotic actions for safety reasons to allow for repair or replacement of the failed mover. This approach requires additional hardware and safety mechanisms to service the failed mover. Thus, a better approach may consist of allowing access to the library without the need for additional safety mechanisms to secure and shield the repair operation, and also not requiring the user to schedule any operational outage.
In a system with redundant movers or robots that operate in an active/passive mode, one mover is active and is designed to perform all motion requests, and the secondary passive mover is on standby to take over in the event the active mover fails. In a system with redundant movers that operate in an active/active mode, both movers perform motion requests. In this type of system, in the event of a mover failure, the library either operates in a degraded mode, failing and affecting only those host requests that required the failed mover, or the library allows the operational mover to take over (sometimes referred to as a “failover”) and perform all motion requests. While the operational mover can continue to operate and service motion requests, host command response handling for a command that failed and initiated a failover request can be disruptive to a host application and cause the host application to fail. User intervention to restart the application and continue operation is one means to continue operation, however, a transparent approach that will not affect host operations and continue operation is desired.